A few years ago, tungsten halogen technology was adapted for use in standard lamps. The new tungsten halogen standard lamps have an inner capsule that contains the tungsten halogen process, and an outer envelope that guards against possible non-passive fracture of the inner capsule, and shields the user from the high surface temperature of the inner capsule. The inner capsule is then mounted on a frame inside the outer envelope, with the frame acting as one of the electrical connections for the inner capsule. Tungsten halogen lamps can produce a higher quality light, be more efficient, and have a longer life than ordinary filamented lamps.
During assembly, the frame and inner capsule are inserted in the outer envelope, and the base is screwed on. The threaded base pinches the exterior arms of the frame against the envelope neck to make electrical contact and hold the frame in place. To make good electrical contact, and to ensure the base is not unthreaded, the frame to base contact has been made by a sharp point, aimed in the threading direction. As the base threads over the frame, the frame points dig progressively deeper into the base. In final position, the frame points are well embedded in the base, ensuring electrical contact, and are pointed against the unthreading of the base to prevent removal of the base. Because of variations in the pointed ends, the lengths of the frame components, molded glass dimensions and similar causes, the frame ends do not always contact the base equally. The frame can then be twisted in the outer envelope, leaving the inner capsule misaligned. This is a cosmetic problem. The misalignment can also be a mechanical problem. The misaligned inner capsule can knock against the outer envelope during shipment and break. The life of the inner capsule may also be affected by the irregular heat flow around the adjacent outer envelope. There is then a need for a support frame that consistently centers the inner capsule in the outer envelope.
The double envelope, tungsten halogen lamps are assembled by hand threading the base to the lamp neck. The torque characteristic of lamps with pointed frame ends is not a linear force, but is an increasing and perhaps even an accelerating force. The high torque need to thread the base to its final position may lead to injuries from repeated high stress of the assemblers' fingers, hands or wrists. By reducing the diameter of the support frame wire, the wire may be made more flexible, but a more flexible wire allows greater sway in the assembled lamp. Greater flexibility in the support frame is also likely to result in a bent, or distorted support frame. There is then a need for a double envelope electric lamp with a low assembly torque support frame for the internal capsule that is unlikely to sway or be distorted.
U.S. Pat. No. 4,647,809 issued to Ronald G. Blaisdell et al on Mar. 3, 1987 for a Electric Lamp with Self-Mounting Frame Assembly and Method of Constructing Same shows a support frame for an internal capsule. Blaisdell suggests using either flat metal pieces or thin wires welded together to form a frame. In both instances the frame ends include projections that cut into the base as the base is screwed onto the outer envelope.